1. Field of the Invention
Example embodiments of the present invention relate to novel organic polymer semiconductor compounds, methods of forming organic polymer semiconductor thin films using the same, and organic thin film transistors (OTFTs) using the same. Various example embodiments of the present invention relate to organic polymer semiconductor compounds having a side chain including (but not limited to), for example, a removable substituent, and/or an OTFT, using the organic polymer semiconductor compounds for an organic active layer.
2. Description of the Related Art
An OTFT may include a substrate, a gate electrode, an insulating layer, source/drain electrodes, and a channel layer. Such an OTFT may be classified into a bottom contact (BC) type OTFT, in which a channel layer may be formed on the source and drain electrodes, and a top contact (TC) type OTFT, in which a metal electrode may be formed on a channel layer.
The channel layer of the OTFT may be formed of an inorganic semiconductor material, for example, silicon (Si). However, according to recent trends toward larger display areas, lower prices and/or improved flexibility of displays, the above-noted channel layer may be made using an organic semiconductor material instead of an inorganic material requiring a conventional high temperature, vacuum manufacturing process.
In recent years, thorough research into an organic semiconductor material for a channel layer of an OTFT has been conducted, and transistor properties of these materials have been reported. Low molecular weight or oligomer type organic semiconductor materials, which have been studied, include, (but are not limited to), for example, melocyanine, phthalocyanine, perylene, pentacene, C60, thiophene oligomer, etc. In addition, a high charge mobility of 3.2-5.0 cm2/Vs or more using pentacene monocrystals was reported. A charge mobility of 0.01-0.1 cm2/Vs and on/off current ratio using an oligothiophene derivative were also reported.
However, the above-noted conventional techniques may be disadvantageous because they involve a process of forming a thin film mainly conducted in a vacuum. Such a process thus undesirably increases the manufacturing costs.
Conventional methods disclose synthesizing regioregular polythiophene P3HT (poly(3-alkylthiophene)) and an OTFT device having charge mobility of 0.01-0.04 cm2/Vs manufactured using the regioregular polythiophene-P3HT. However, the regioregular polythiophene P3HT, having a charge mobility of about 0.01 cm2/Vs, may be unstable in air and thus may have a high cut-off leakage current (10−9 A or more), resulting in a lower on/off current ratio of 400 or less. Consequently, the above material may be unsuitable or undesirable for application in electronic devices. In addition, although conventional methods disclose an OTFT device using a polythiophene derivative having increased solubility, they may have at least some shortcomings, for example, a low charge mobility, despite having low leakage current.